1. Field of the Invention
The present invention relates to the field of isolation systems and gravel pack assemblies for use in a wellbore. More particularly, the invention provides an improved system and method for zone isolation following gravel pack completions installed in a wellbore.
2. Description of the Prior Art
Typical prior art isolation systems involve intricate positioning of tools which are installed down-hole after the gravel pack. An example of this type of system is available from Baker. This system utilizes an anchor assembly which is run into the well bore after the gravel pack. The anchor assembly is released by a shearing action, and subsequently latched into position.
Certain disadvantages have been identified with these systems. For example, prior conventional isolation systems have had to be installed after the gravel pack, thus requiring greater time and extra trips to install the isolation assemblies. Also, prior systems have involved the use of fluid loss control pills after gravel pack installation, and have required the use of thru-tubing perforation or mechanical opening of a wireline sliding sleeve to access alternate or primary producing zones. Since multiple trips into the well are required for gravel pack and isolation, these systems are time consuming methods and provide less flexibility and reliability.
An example of an isolation washpipe for well completions is disclosed in U.S. Pat. No. 5,343,949, incorporated herein by reference. In this system, there is an expansion joint which is used to push a closing sleeve into a closed position over the production screen.
More recently, isolation systems have been developed which do not require the running of tailpipe and isolation tubing separately. Instead, the system uses the same pipe to serve both functions: as tailpipe for circulating-style treatments and as production/isolation tubing. An example of this type of isolation system is disclosed in U.S. Pat. No. 5,865,251, incorporated herein by reference. An isolation sleeve is installed inside the production screen at surface and placed in the wellbore simultaneously with the service tool. The isolation sleeve is thereafter controlled in the wellbore by means of the inner service string. This system is adapted for well control purposes and for well bore fluid loss control. It combines simplicity, reliability, safety and economy, while also affording flexibility in use.
However, '251 provides only small orifices for circulation of the gravel pack fluid through the isolation sleeve. Further, '251 allows debris to become trapped between the production screen and the isolation sleeve. Further, because the washpipe extends through the isolation sleeve during the gravel pack operation, there is the possibility that debris will become lodged between the isolation sleeve and the wash pipe. This debris could cause the washpipe to hang or jam upon withdrawal so that the entire service string is permanently lodged in the isolation sleeve. Therefore, there is a need for a system which allows the isolation sleeve to be closed without a washpipe extending through the isolation sleeve. Further, there is a need for an isolation sleeve which does not allow debris to become accumulated between the isolation sleeve and the production screen and which allows fluid to freely pass through the isolation sleeve during the gravel pack operation.